36. Note on the absorption of gases, vapours, and substances 



in solution by solids and amorphous substances. 



By MoBRis W. Trayers, D.Sc, F.R.S., 



Director of the Indian Institute of Science^ Bangalore. 



Undex' the heading which foi'ms the title of this paper may be 

 inclixded the phenomena which underlie many of the problems 

 which are at present engaging the attention of scientific workers 

 in India. The absorption and retention of water in various ma- 

 terials is a subject which is naturally of particular interest in a 

 coimtry which presents snch varied conditions of climate, and 

 perhaps the elucidation of the general principles of the phenomena 

 concerned may assist in the solution of some of the ecomomie 

 questions; which are now under investigation. 



Amorjplioiiii and solid ■^-uhstauce.^. 



It is necessary for the purposes of the present discussion to 

 make a distinction between true solids and amorphous substances. 

 We 'recognise three states, or in modern language * phases' of 

 matter, the solid, the liquid, and the gaseous. When a liquid 

 is cooled it will ultimately become changed into a crystalline sub- 

 stance, a solid, and at the transition point there will be a marked 

 discontinuity in its properties; or as the temperature falls it 

 will merely become more viscous, and will at length become to all 

 appearances a solid, without however exhibiting any discontinuity 

 whatsoever in its properties. Amorphous substances such as glass, 

 which are formed in this manner, are really in the ^liquid phase,' 



and are only solids in the popular sense. They always exhibit a 

 tendency to pass into the more stable * solid phase,' tliough the 

 change often takes place with excessive slowness. An example of 

 this is to be found in the glass of old church windows in England 

 which sometimes begins to crumble ; and when once the decay sets 

 in it cannot be arrested. 



There is another manner in which amorphous substances may 

 be formed. When a substance separates from solution it is the 

 most unstable form which is first produced. Thus, calcium car- 

 bonate is precipitated from a mixture of solutions of calcium chlo- 

 lide and ammonium rarbonate in the form of liquid, or at least 

 amorphous, globules, which i^apidly become crystalline. Highly 

 complex orgnnic substances, when precipitated in this manner, 

 often retain their amorphous character, and do not become crystal- 

 line. Such is the character and mode of formation of the fibrous 

 material of plants. 



